Transcutaneous Electrical Nerve Stimulation (also see Chapter 73 )

TENS is thought to reduce pain by nociceptive inhibition at a presynaptic level in the dorsal horn by limiting central transmission. Electrical stimulation preferentially activates low-threshold myelinated nerves. Afferent inhibition effects inhibit propagation of nociception along unmyelinated small "c" fibers by blocking impulses to target cells in the substantia gelatinosa of the dorsal horn. TENS is also thought to enhance release of endorphins and dynorphins centrally. ^[67] Placement of electrode pads over the lower back region in the distribution of T10-L1 provides analgesia for some patients in early labor.^[68] However, other reports have failed to demonstrate its effectiveness for labor analgesia or as an adjunct to epidural analgesia.^{[69] [70]}